vim-patch:9.0.0370: cleaning up afterwards can make a function messy

Problem:    Cleaning up afterwards can make a function messy.
Solution:   Add the :defer command.

1d84f7608f

Omit EX_EXPR_ARG: Vim9 script only.
Make :def throw E319 to avoid confusing behavior.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/ex_cmds.lua

@@ -714,6 +714,18 @@ module.cmds = {
     addr_type='ADDR_OTHER',
     func='ex_debuggreedy',
   },
+  {
+    command='def',
+    flags=bit.bor(EXTRA, BANG, SBOXOK, CMDWIN, LOCK_OK),
+    addr_type='ADDR_NONE',
+    func='ex_ni',
+  },
+  {
+    command='defer',
+    flags=bit.bor(NEEDARG, EXTRA, NOTRLCOM, CMDWIN, LOCK_OK),
+    addr_type='ADDR_NONE',
+    func='ex_call',
+  },
   {
     command='delcommand',
     flags=bit.bor(BANG, NEEDARG, WORD1, TRLBAR, CMDWIN, LOCK_OK),